CN114318465B - Micro-arc oxidation preparation method for 7-series aluminum alloy black surface - Google Patents
Micro-arc oxidation preparation method for 7-series aluminum alloy black surface Download PDFInfo
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- GCLGEJMYGQKIIW-UHFFFAOYSA-H sodium hexametaphosphate Chemical compound [Na]OP1(=O)OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])O1 GCLGEJMYGQKIIW-UHFFFAOYSA-H 0.000 claims description 16
- 235000019982 sodium hexametaphosphate Nutrition 0.000 claims description 16
- 239000001577 tetrasodium phosphonato phosphate Substances 0.000 claims description 16
- 239000004115 Sodium Silicate Substances 0.000 claims description 15
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims description 15
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- 229910052802 copper Inorganic materials 0.000 claims description 4
- 239000010949 copper Substances 0.000 claims description 4
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 4
- 239000011701 zinc Substances 0.000 claims description 4
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 2
- 238000010668 complexation reaction Methods 0.000 claims description 2
- MEFBJEMVZONFCJ-UHFFFAOYSA-N molybdate Chemical compound [O-][Mo]([O-])(=O)=O MEFBJEMVZONFCJ-UHFFFAOYSA-N 0.000 claims description 2
- 229910052760 oxygen Inorganic materials 0.000 claims description 2
- 239000001301 oxygen Substances 0.000 claims description 2
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- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
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Abstract
The invention discloses a micro-arc oxidation preparation method of a 7-series aluminum alloy black surface, wherein the 7-series aluminum alloy surface prepared by the method is black, complete, fine and smooth and high in hardness. S1: setting micro-arc oxidation parameters, and immersing a workpiece to be treated in electrolyte for micro-arc oxidation treatment; the micro-arc oxidation parameters comprise positive current density, negative current density, pulse frequency, pulse width, duty ratio and micro-arc oxidation time, a power supply used for micro-arc oxidation is bipolar pulse current, the power supply output mode of micro-arc oxidation is eight-step sectional steady-flow output, in the eight-step sectional steady-flow output, positive current density is gradually increased, negative current density is only applied at sixth to eighth steps, and negative current density is gradually increased; s2: and (3) cleaning and drying the workpiece processed in the step (S1).
Description
Technical Field
The invention relates to the technical field of aluminum alloy surface treatment, in particular to a micro-arc oxidation preparation method of a 7-series aluminum alloy black surface.
Background
The aluminum alloy has very good physical, chemical, mechanical and processing properties, so that the aluminum alloy has a wide application range and good application prospect. Meanwhile, the aluminum alloy is an amphoteric metal, has low surface hardness, and particularly has poor corrosion resistance of 7-series aluminum alloy, and can be corroded in acidic medium and alkaline medium. In order to make the aluminum alloy widely applicable, a metal plating layer or an organic coating layer is generally prepared on the surface of the aluminum alloy by surface treatment methods such as electroplating, electrophoresis, spraying and the like, and the color and the performance of the surface of the aluminum alloy are modified to improve the performances such as hardness, corrosion resistance and the like of the aluminum alloy. Common aluminum alloy surface treatment methods include anodic oxidation coloring techniques and micro-arc oxidation coloring techniques.
In the related art, the anodic oxidation coloring technology of aluminum alloy can be broadly divided into three categories, namely a chemical coloring method, an integral coloring method and an electrolytic coloring method. By adopting the chemical dyeing method, the anodic oxide film has porosity and chemical activity, and coloring substances and pigment bodies in the oxide film are positioned on the top of the oxide film, so that substances in the dyeing liquid can be adsorbed, and chemical reaction is carried out on the surface of the oxide film to generate the coloring substances so as to color the oxide film. The coloring matter and pigment are uniformly dispersed in the whole oxide film by adopting the integral coloring method. The integral color development method is different from the chemical dyeing method and the electrolytic coloring method in that the method has the characteristics of film formation and color development, namely, a colored oxide film is directly generated by anodic electrolytic treatment in electrolyte. The electrolytic coloring is usually secondary electrolytic coloring, namely, firstly oxidizing the aluminum material by a conventional acid method, then immersing the aluminum material in a solution containing metal salt for electrolytic coloring treatment, penetrating metal cations into pinholes of the oxide film under the action of an electric field, and reducing and depositing the metal cations at the bottoms of the pinholes so as to color the oxide film. The color of the electrolytically colored film depends not only on the kind of deposited metal, but also is closely related to the uniformity, hole depth and shape of the film. This is because the chromogenic cause of electrolytic coloring is a result of light scattering on the surface of the deposited metal particles, and the scattering effect of light is affected by various factors such as the kind of metal and the size and shape of the deposited particles.
The micro-arc oxidation coloring technology is used for treating the aluminum alloy, so that the aluminum alloy has rich colors and the corrosion resistance of the aluminum alloy can be improved. However, after the treatment of the prior art, the surface of the aluminum alloy is rough, the material is brittle and the color is uneven.
For a 7-series aluminum alloy such as 7075 aluminum alloy, the main alloying element is zinc, and also contains impurity elements such as copper, magnesium, manganese, and the like. The addition of these elements improves the texture properties of the material, and the mechanical strength and properties of the material can be improved by heat treatment, but the disadvantage is that the corrosion resistance of the material is not strong and the surface hardness is not high. For some special application fields such as firearms and transmitters in military equipment, the appearance of the equipment is dark black and even needs to have light absorption performance, after common process treatment, the surface of an aluminum alloy material is rough and not wear-resistant, so that an expensive wear-resistant coating is additionally sprayed on the surface of the equipment to enable the surface of the aluminum alloy to be black, and meanwhile, the requirement of wear resistance is met.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a micro-arc oxidation preparation method for the black surface of a 7-series aluminum alloy, wherein the 7-series aluminum alloy prepared by the method is black, complete, fine and smooth and high in hardness.
The purpose of the invention is realized in the following way:
a preparation method of a 7-series aluminum alloy black surface by micro-arc oxidation comprises the following steps:
s1: setting micro-arc oxidation parameters, and immersing a workpiece to be treated in electrolyte for micro-arc oxidation treatment;
the micro-arc oxidation parameters comprise positive current density, negative current density, pulse frequency, pulse width, duty ratio and micro-arc oxidation time, the power supply used for micro-arc oxidation is bipolar pulse current, the power supply output mode of micro-arc oxidation is eight-step sectional steady-flow output, in the eight-step sectional steady-flow output, positive current density is gradually increased, negative current density is only applied at sixth to eighth steps, and negative current density is gradually increased,
in the eight-step sectional steady flow output mode, a micro-thin oxide layer can be formed on the surface of the aluminum alloy, the resistance becomes larger along with the thickening of the oxide layer, negative current is applied while positive current density is increased, the follow-up micro-arc oxidation is facilitated, in the eight-step sectional steady flow output process, common aluminum oxide is generated on the surface of the aluminum alloy at the initial stage, and the aluminum oxide is gradually converted from gamma phase to stable alpha phase along with the increase of the step number at the later stage,
s2: and (3) cleaning and drying the workpiece processed in the step (S1).
Preferably, in step S1, the surface of the workpiece to be treated immersed in the electrolyte is 5cm to 15cm from the liquid level.
Preferably, in step S1, the eight-step segment steady flow output parameters are:
first step forward current: 50-100A, negative current: 0A;
second step forward current: 50-150A, negative current: 0A;
third step forward current: 50-150A, negative current: 0A;
fourth step forward current: 50-150A, negative current: 0A;
fifth step forward current: 80-160A, negative current: 0A;
sixth step forward current: 100A-200A, negative current: 10A to 30A;
seventh step forward current: 100A-200A, negative current: 15A-40A;
eighth step forward current: 100A-200A, negative current: 15A-40A;
the positive current density is 0.3-2.0A/cm 2 The negative current density is 0 to 0.3A/cm 2 。
Further, the positive current density is 0.5-1.8A/cm 2 The negative current density is 0.07-0.18A/cm 2 。
Further, the positive current density is 1.2-1.6A/cm 2 The negative current density is 0.07-0.15A/cm 2 。
Further, the positive current density is 1.5A/cm 2 Negative current density of 0.15A/cm 2 。
Preferably, in step S1, the pulse frequency is 1500Hz to 2000Hz.
Further, the pulse frequency is 1600 Hz-1800 Hz.
Further, the pulse frequency is 1700Hz.
Preferably, in step S1, the pulse width is 150 μs to 250 μs.
Preferably, in step S1, the duty cycle is 10% to 20%.
Preferably, in step S1, the micro-arc oxidation time is 30min to 50min.
Preferably, in step S1, the temperature of the electrolyte is 20 to 35 ℃, the pH of the electrolyte is 9.5 to 12.0, and potassium hydroxide is added for adjustment when the pH of the electrolyte is less than 9.5. If the pH of the electrolyte is higher than 12, ablation occurs to cause defects.
Further, the pH of the electrolyte is 10.0 to 12.0.
Further, the pH of the electrolyte is 10.0 to 11.0.
Preferably, the electrolyte comprises 6-12 g/L of sodium hexametaphosphate, 6-11 g/L of sodium silicate, 8-15 g/L of sodium metavanadate, 10-25 g/L of sodium molybdate and 1-5 g/L of potassium hydroxide;
further, the addition amount of the sodium hexametaphosphate is 6 g/L-10 g/L.
Further, the addition amount of the sodium hexametaphosphate is 6.5 g/L-9.5 g/L.
Further, the addition amount of the sodium hexametaphosphate is 7 g/L-9 g/L.
Further, the addition amount of the sodium hexametaphosphate is 8g/L.
Further, the addition amount of the sodium silicate is 6g/L to 10g/L.
Further, the addition amount of the sodium silicate is 7g/L to 10g/L.
Further, the addition amount of the sodium silicate is 8g/L to 10g/L.
Further, the addition amount of the sodium silicate is 9g/L to 10g/L.
Further, the addition amount of the sodium silicate is 9g/L.
Further, the addition amount of the sodium metavanadate is 8 g/L-13 g/L.
Further, the addition amount of the sodium metavanadate is 9 g/L-12 g/L.
Further, the addition amount of the sodium metavanadate is 10 g/L-12 g/L.
Further, the addition amount of the sodium metavanadate is 11g/L.
Further, the addition amount of the sodium molybdate is 10g/L to 20g/L.
Further, the addition amount of the sodium molybdate is 12g/L to 18g/L.
Further, the addition amount of the sodium molybdate is 13g/L to 17g/L.
Further, the addition amount of the sodium molybdate is 14g/L to 16g/L.
Further, the addition amount of the sodium molybdate is 15g/L.
Further, the addition amount of the potassium hydroxide is 1g/L to 9g/L.
Further, the addition amount of the potassium hydroxide is 1g/L to 5g/L.
Further, the addition amount of the potassium hydroxide is 2g/L to 6g/L.
Further, the addition amount of the potassium hydroxide is 3g/L.
The preparation method of the electrolyte comprises the following steps: sequentially dissolving sodium hexametaphosphate, sodium silicate, sodium metavanadate, sodium molybdate and potassium hydroxide in water according to a proportion to form an alkaline electrolyte;
the film forming speed of the oxide layer protective film and the corrosion resistance of the protective film are improved through sodium hexametaphosphate; the sodium silicate is distributed at the part of the protective film close to the matrix, so that the sealing property of the protective film is ensured; sodium metavanadate and sodium hexametaphosphate cooperate with each other, so that the film forming speed of the protective film and the corrosion resistance of the protective film are improved; the sodium molybdate improves the wear resistance, and the sodium molybdate contains multiple oxygen to meet the requirement of micro-arc oxidation, in addition, the sodium molybdate has complexation, copper and zinc dissolved from aluminum alloy can be complexed in the form of molybdate complex, and become sticky precipitate, so that the quality of a finished product of micro-arc oxidation is not affected, and the service life of the functional plating solution is prolonged; the potassium hydroxide has high conductivity and good conductivity, and the reliability of the functional plating solution is improved.
Preferably, the workpiece to be processed is a gun or a transmitter.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
the micro-arc oxidation preparation method provided by the invention is used for forming a black ceramic oxide film on the surface of the 7-series aluminum alloy rapidly when the surface of the 7-series aluminum alloy is treated, so that the surface of the 7-series aluminum alloy has fine surface quality while being black, has good wear resistance, and is suitable for preparing equipment with high precision requirements. Meanwhile, the surface of the treated aluminum alloy has better wear resistance and corrosion resistance, and the surface hardness can reach more than HV 750. The better wear resistance is generated by the synergistic effect of a ceramic layer with high hardness formed on the surface, a smaller roughness Ra value and sodium molybdate in the electrolyte. The better corrosion resistance is achieved because the surface of the material treated by the micro-arc oxidation preparation method is denser and has fewer pores than the surface of the material treated by the common micro-arc oxidation preparation method, and the surface of the material treated by the common micro-arc oxidation preparation method is usually porous.
The preparation method of micro-arc oxidation provided by the invention can directly form a uniform black micro-arc oxidation ceramic layer on the surface of aluminum alloy. Under the D65 light source, the appearance is uniform and fine, the glossiness is good, the material is suitable for different application environments, and the requirements of special functional materials such as light absorption materials and materials for precision equipment are met. No additional coloring is required, nor is painting required. The paint is saved, the cost is reduced, and the environment is protected.
The power output mode of the micro-arc oxidation preparation method provided by the invention is eight-step sectional steady-flow output, and compared with the common micro-arc oxidation, the power consumption is smaller, and the cost is further reduced.
According to the preparation method of micro-arc oxidation, the electrolyte used is alkaline electrolyte, and compared with conventional acidic electrolyte, the preparation method of micro-arc oxidation has better environmental friendliness.
The power output mode of the micro-arc oxidation preparation method provided by the invention is eight-step sectional steady-flow output. In the eight-step segmented steady-flow output, the positive current density gradually increases, and the negative current is applied only at the sixth to eighth steps. Compared with a constant-current mode, the eight-step sectional steady-flow output has the advantages that on one hand, the early-stage electricity consumption is small, and the electricity consumption and energy consumption are saved; on the other hand, in the eight-step sectional steady-flow output mode, a micro-thin oxide layer can be formed on the surface of the aluminum alloy, and the resistance becomes larger along with the thickening of the oxide layer, so that negative current is applied while positive current density is increased, and the follow-up micro-arc oxidation is facilitated. In the eight-step sectional steady flow output process, common alumina is firstly generated on the surface of the aluminum alloy, and the alumina is gradually converted from gamma phase to stable alpha phase along with the increase of the step number in the later stage.
The micro-arc oxidation preparation method of the 7-series aluminum alloy black surface is suitable for surface treatment of special equipment, such as firearms, transmitters and the like, has higher privacy requirements, and the surface material needs to have light absorption performance and is dark black. Therefore, after conventional anodic oxidation, an additional process is required for coloring (the gun must be dark black to prevent reflection).
The preparation method of the 7-series aluminum alloy black surface by micro-arc oxidation has simple technical process. Micro-arc oxidation does not need a complex and strict pretreatment process, and is more suitable for extensive large-scale industrial production conditions. In addition, the common anodic oxide film generally needs hole sealing treatment to further improve the corrosion resistance of the film, and the micro-arc oxide film prepared by the preparation method provided by the invention is thicker in film and higher in corrosion resistance and hardness, so that the requirements of daily use can be met without post-treatment.
The preparation method of the micro-arc oxidation of the black surface of the 7-series aluminum alloy has better adaptability to materials subjected to micro-arc oxidation. The current anodic oxidation technology is only suitable for deformed aluminum alloys with low Si content, and for cast aluminum alloys with high Si content, the anodic oxidation film layer structure is uneven, and the performance is difficult to meet the use requirement. In the preparation method, high temperature of thousands of ℃ can be instantaneously generated in the micro-arc oxidation process, and Si in the matrix material can be oxidized to form a part of the film layer, so that adverse influence of Si on the film layer is eliminated. In addition, anodic oxidation can only be applied to surface treatment of valve metals such as Mg, al, ti and the like, and the micro-arc oxidation can also be applied to surface treatment of steel under special conditions.
The preparation method of the 7-series aluminum alloy black surface by micro-arc oxidation has the advantage that the electrolyte used by micro-arc oxidation is more environment-friendly. At present, the surface treatment technologies such as chemical conversion, electroplating, anodic oxidation and the like mostly use acid electrolyte, and the electrolyte treatment carelessly causes serious pollution to the environment. The micro-arc oxidation preparation method uses alkaline electrolyte, and the pollution of electrolyte waste liquid to the environment is small.
The micro-arc oxidation preparation method of the 7-series aluminum alloy black surface has better function designability. The micro-arc oxidation film with different performance requirements can be prepared by adjusting the composition of the electrolyte and the configuration of the electric parameters. Is particularly suitable for the field of military aviation.
The 7-series aluminum alloy contains impurity elements such as zinc, copper, magnesium and the like, and after being processed by other methods, the surface is rough, the color is uneven, the binding force is poor, the material is brittle, and the block-shaped material is easy to fall off. The ordinary micro-arc is oxidized to grey or grey white, and a layer of wear-resistant paint is sprayed on the surface to turn black. And the cost of the wear-resistant paint is high, and the market price is about 3000 yuan per kilogram. The micro-arc oxidation preparation method directly omits the wear-resistant paint, greatly reduces the production cost for enterprises and reduces the environmental pollution.
The common anodic oxidation and micro-arc oxidation require about 8 hours, and the preparation method of the 7-series aluminum alloy black surface has the advantages that the treatment time of the whole process is 30-50 minutes according to the size of a workpiece, so that the energy consumption is greatly reduced.
The micro-arc oxidation preparation method of the 7-series aluminum alloy black surface can form a film layer with the thickness of 30-50 mu m on the 7-series aluminum alloy surface, solves the problems of surface hardness, wear resistance and corrosion resistance of the 7-series aluminum alloy, and the hardness can reach over HV 750.
After the 7-series aluminum alloy is treated by the micro-arc oxidation preparation method, the surface is compact, the glossiness is good, and the surface roughness Ra is less than 1.6.
The 7-series aluminum alloy treated by the micro-arc oxidation preparation method of the invention rapidly forms a black protective film on the surface, wherein the part close to the substrate in the protective film mainly comprises common alumina, and the middle part is alpha-phase Al 2 O 3 And gamma-phase Al 2 O 3 The surface is alpha phase Al 2 O 3 。
Drawings
Fig. 1 is a scanning electron microscope image of a 7075 aluminum alloy casing body after surface treatment.
Fig. 2 is a scanning electron microscope image of a cross section of a 7075 aluminum alloy casing body after surface treatment.
Detailed Description
The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described with reference to the embodiments, but the present invention is not limited to these embodiments.
Example 1
In this example, 21 upper casing bodies made of 7075 aluminum alloy were treated, and the surface area of the upper casing bodies was 5dm2. The method specifically comprises the following steps:
s1: preparing electrolyte;
s2: setting micro-arc oxidation parameters, and immersing a workpiece to be treated in the electrolyte for treatment;
s3: cleaning and drying the workpiece processed in the step S2;
before step S1, the surface of the workpiece to be processed is preprocessed, wherein the preprocessing steps are as follows: water washing, degreasing, water washing, light removal, water washing, weak corrosion and water washing.
The current of the micro-arc oxidation preparation method is bipolar pulse current.
In step S2, the surface of the workpiece to be treated immersed in the electrolyte is 10cm from the liquid level.
The pulse frequency was 1700Hz. The pulse width was 200 mus. The duty cycle is 15%. The micro-arc oxidation time is 50min. The temperature of the electrolyte was 20 ℃.
The power output mode of the micro-arc oxidation preparation method is eight-step sectional steady-flow output.
The parameters of the eight-step segmented steady flow output are shown in table 1.
Table 1 shows eight-step sectional steady flow output parameters for the casing
Where current density magnitude = current magnitude/number of samples/sample surface area.
The electrolyte comprises 9g/L of sodium hexametaphosphate, 8g/L of sodium silicate, 12g/L of sodium metavanadate, 17g/L of sodium molybdate and 3g/L of potassium hydroxide.
Example 2
In this example, 30 pieces of 7075 aluminum alloy composite reed pipes were treated, and the surface area of the composite reed pipes was 4.5dm2. The method specifically comprises the following steps:
s1: preparing electrolyte;
s2: setting micro-arc oxidation parameters, and immersing a workpiece to be treated in the electrolyte for treatment;
s3: cleaning and drying the workpiece processed in the step S2;
before step S1, the surface of the workpiece to be processed is preprocessed, wherein the preprocessing steps are as follows: water washing, degreasing, water washing, light removal, water washing, weak corrosion and water washing.
The current of the micro-arc oxidation preparation method is bipolar pulse current.
In step S2, the surface of the workpiece to be treated immersed in the electrolyte is 10cm from the liquid level.
The pulse frequency was 1700Hz. The pulse width was 200 mus. The duty cycle is 15%. The micro-arc oxidation time is 50min. The temperature of the electrolyte was 20 ℃.
The power output mode of the micro-arc oxidation preparation method is eight-step sectional steady-flow output.
The parameters of the eight-step segmented steady flow output are shown in table 2.
TABLE 2 eight-step segmented steady flow output parameters for compound reed pipe
Where current density magnitude = current magnitude/number of samples/sample surface area.
The electrolyte comprises 9g/L of sodium hexametaphosphate, 8g/L of sodium silicate, 12g/L of sodium metavanadate, 17g/L of sodium molybdate and 3g/L of potassium hydroxide.
Example 3
In this example, 21 lower cases made of 7075 aluminum alloy were treated, and the surface area of the lower cases was 4.9dm 2 . The method specifically comprises the following steps:
s1: preparing electrolyte;
s2: setting micro-arc oxidation parameters, and immersing a workpiece to be treated in the electrolyte for treatment;
s3: cleaning and drying the workpiece processed in the step S2;
before step S1, the surface of the workpiece to be processed is preprocessed, wherein the preprocessing steps are as follows: water washing, degreasing, water washing, light removal, water washing, weak corrosion and water washing.
The current of the micro-arc oxidation preparation method is bipolar pulse current.
In step S2, the surface of the workpiece to be treated immersed in the electrolyte is 10cm from the liquid level.
The pulse frequency was 1700Hz. The pulse width was 200 mus. The duty cycle is 15%. The micro-arc oxidation time was about 58 minutes. The temperature of the electrolyte was 20 ℃.
The power output mode of the micro-arc oxidation preparation method is eight-step sectional steady-flow output.
The parameters of the eight-step segmented steady flow output are shown in table 3.
Table 3 lower case eight-step subsection steady flow output parameters
Where current density magnitude = current magnitude/number of samples/sample surface area.
The electrolyte comprises 9g/L of sodium hexametaphosphate, 8g/L of sodium silicate, 12g/L of sodium metavanadate, 17g/L of sodium molybdate and 3g/L of potassium hydroxide.
Example 4
In this example, 84 buffer tubes of 7075 aluminum alloy were treated, and the surface area of the buffer tube was 0.78dm2. The method specifically comprises the following steps:
s1: preparing electrolyte;
s2: setting micro-arc oxidation parameters, and immersing a workpiece to be treated in the electrolyte for treatment;
s3: cleaning and drying the workpiece processed in the step S2;
before step S1, the surface of the workpiece to be processed is preprocessed, wherein the preprocessing steps are as follows: water washing, degreasing, water washing, light removal, water washing, weak corrosion and water washing.
The current of the micro-arc oxidation preparation method is bipolar pulse current.
In step S2, the surface of the workpiece to be treated immersed in the electrolyte is 10cm from the liquid level.
The pulse frequency was 1700Hz. The pulse width was 200 mus. The duty cycle is 15%. The micro-arc oxidation time was about 40 minutes. The temperature of the electrolyte was 20 ℃.
The power output mode of the micro-arc oxidation preparation method is eight-step sectional steady-flow output.
The parameters of the eight-step segmented steady flow output are shown in table 4.
TABLE 4 buffer tube eight step segment steady flow output parameters
Where current density magnitude = current magnitude/number of samples/sample surface area.
The electrolyte comprises 9g/L of sodium hexametaphosphate, 8g/L of sodium silicate, 12g/L of sodium metavanadate, 17g/L of sodium molybdate and 3g/L of potassium hydroxide.
Comparative example 1
The difference between the comparative example and the example 1 is that the power output mode of the micro-arc oxidation preparation method is constant current output, and the ratio of positive current to negative current density is 1:6.
The parameters outputted are shown in table 5.
TABLE 5 constant current micro-arc oxidation output parameters
| Forward current density/A/dm 2 | Negative current density/A/dm 2 | Time/s |
| 2 | 12 | 3000 |
Comparative example 2
The difference between the comparative example and the example 1 is that the power output mode of the micro-arc oxidation preparation method is constant current output, and the ratio of positive current to negative current density is 2:1.
The parameters output are shown in table 6.
TABLE 6 constant current micro-arc oxidation output parameters
| Forward current density/A/dm 2 | Negative current density/A/dm 2 | Time/s |
| 4 | 2 | 3000 |
Comparative example 3
This comparative example differs from example 1 in that sodium molybdate was not added to the electrolyte.
Performance testing
The 7075 aluminum alloy parts treated in examples 1 to 4 and comparative examples 1 and 2 were tested for their appearance color, hardness, corrosion resistance, roughness, and abrasion resistance, respectively.
Wherein, the color and appearance are observed under the D65 standard light source.
The wear resistance is carried out by a friction test, the specification of a sample piece is processed into 30mm multiplied by 20mm multiplied by 3mm, the grinding head is made of tungsten steel, the frequency is 100 times/min, the load is 9.8N, and the stroke is reciprocating. After the 15min friction test, the substrate material which did not leak out was judged to be acceptable, and the substrate metal was judged to leak out to be unacceptable.
Corrosion resistance was tested by the method and conditions specified in GB/T10125 for a period of 236h.
The results are shown in Table 7.
TABLE 7 results of surface Performance test
| Color, appearance | Wear resistance | hardness/HV | Corrosion resistance | Roughness Ra/. Mu.m | |
| Example 1 | Uniform black, fine and smooth | Qualified product | 800 | Rust-free | 1.3 |
| Example 2 | Uniform black, fine and smooth | Qualified product | 797 | Rust-free | 1.17 |
| Example 3 | Uniform black, fine and smooth | Qualified product | 823 | Rust-free | 1.27 |
| Example 4 | Uniform black, fine and smooth | Qualified product | 760 | Rust-free | 1.35 |
| Comparative example 1 | Black and rough surface | Failure to pass | 693 | Slightly rust | 7.3 |
| Comparative example 2 | Black and rough surface | Failure to pass | 580 | Rust corrosion | 3.12 |
| Comparative example 3 | Uneven black | Failure to pass | 387 | Slightly rust | 1.91 |
In addition, the surface morphology of the upper casing body treated in example 1 was also observed by a scanning electron microscope, as shown in fig. 1. As can be seen from the figure, the upper casing surface microstructure is dense, and no significant porosity is observed. Further observing the shape of the cross section of the surface of the workpiece of the upper casing body, as shown in fig. 2, it can be seen from fig. 2 that the workpiece is subjected to the surface treatment of the plating solution of the invention to form a protective layer, the protective layer is divided into two layers, the interface between the layers is continuous, and the thickness is 30-70 μm.
The micro-arc oxidation preparation method of the 7-series aluminum alloy black surface greatly reduces the power consumption and energy consumption due to the adoption of eight-step segmented steady-flow output, omits expensive wear-resistant paint, and has the cost of about 10.2 yuan/dm 2 Reduced to 3.3 yuan/dm 2 The cost is obviously reduced. Finally, it is noted that the above-mentioned preferred embodiments are only intended to illustrate rather than limit the invention, and that, although the invention has been described in detail by means of the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.
Claims (8)
1. The preparation method of the 7-series aluminum alloy black surface by micro-arc oxidation is characterized by comprising the following steps of:
s1: setting micro-arc oxidation parameters, and immersing a workpiece to be treated in electrolyte for micro-arc oxidation treatment;
the micro-arc oxidation parameters comprise positive current density, negative current density, pulse frequency, pulse width, duty ratio and micro-arc oxidation time, the power supply used for micro-arc oxidation is bipolar pulse current, the power supply output mode of micro-arc oxidation is eight-step sectional steady-flow output, in the eight-step sectional steady-flow output, positive current density is gradually increased, negative current density is only applied at sixth to eighth steps, and negative current density is gradually increased,
in the eight-step sectional steady flow output mode, a micro-thin oxide layer can be formed on the surface of the aluminum alloy, the resistance becomes larger along with the thickening of the oxide layer, negative current is applied while positive current density is increased, the follow-up micro-arc oxidation is facilitated, in the eight-step sectional steady flow output process, common aluminum oxide is generated on the surface of the aluminum alloy at the initial stage, and the aluminum oxide is gradually converted from gamma phase to stable alpha phase along with the increase of the step number at the later stage,
the electrolyte comprises 6g/L to 12g/L of sodium hexametaphosphate, 6g/L to 11g/L of sodium silicate, 8g/L to 15g/L of sodium metavanadate, 10g/L to 25g/L of sodium molybdate and 1g/L to 5g/L of potassium hydroxide,
the positive current density is 0.3-2.0A/dm 2 The negative current density is 0 to 0.3A/dm 2 ，
The pulse frequency is 1500 Hz-2000 Hz,
the duty ratio is 10% -20%;
s2: and (3) cleaning and drying the workpiece processed in the step (S1).
2. The method for preparing the black surface of the 7-series aluminum alloy by micro-arc oxidation according to claim 1, wherein in the step S1, the surface of the workpiece to be treated immersed in the electrolyte is 5 cm-15 cm away from the liquid level.
3. The method for preparing the black surface of the 7-series aluminum alloy by micro-arc oxidation according to claim 1, wherein in the step S1, eight-step segmentation steady-flow output parameters are as follows:
first step forward current: 50-100A, negative current: 0A;
second step forward current: 50-150A, negative current: 0A;
third step forward current: 50-150A, negative current: 0A;
fourth step forward current: 50-150A, negative current: 0A;
fifth step forward current: 80-160A, negative current: 0A;
sixth step forward current: 100A-200A, negative current: 10A to 30A;
seventh step forward current: 100A-200A, negative current: 15A-40A;
eighth step forward current: 100A-200A, negative current: 15A to 40A.
4. The method for preparing black surface of 7-series aluminum alloy by micro-arc oxidation according to claim 1, wherein in the step S1, the pulse width is 150 μs to 250 μs.
5. The method for preparing the black surface of the 7-series aluminum alloy by micro-arc oxidation according to claim 1, wherein in the step S1, the micro-arc oxidation time is 30-50 min.
6. The method for preparing black surface of 7-series aluminum alloy by micro-arc oxidation according to claim 1, wherein in the step S1, the temperature of the electrolyte is 20-35 ℃, the pH of the electrolyte is 9.5-12.0, and potassium hydroxide is added for adjustment when the pH of the electrolyte is lower than 9.5.
7. The method for preparing the black surface of 7-series aluminum alloy by micro-arc oxidation according to claim 1 or 6, wherein,
the preparation method of the electrolyte comprises the following steps: sequentially dissolving sodium hexametaphosphate, sodium silicate, sodium metavanadate, sodium molybdate and potassium hydroxide in water according to a proportion to form an alkaline electrolyte;
the film forming speed of the oxide layer protective film and the corrosion resistance of the protective film are improved through sodium hexametaphosphate; the sodium silicate is distributed at the part of the protective film close to the matrix, so that the sealing property of the protective film is ensured; sodium metavanadate and sodium hexametaphosphate cooperate with each other, so that the film forming speed of the protective film and the corrosion resistance of the protective film are improved; the sodium molybdate improves the wear resistance, and the sodium molybdate contains multiple oxygen to meet the requirement of micro-arc oxidation, in addition, the sodium molybdate has complexation, copper and zinc dissolved from aluminum alloy can be complexed in the form of molybdate complex, and become sticky precipitate, so that the quality of a finished product of micro-arc oxidation is not affected, and the service life of the functional plating solution is prolonged; the potassium hydroxide has high conductivity and good conductivity, and the reliability of the functional plating solution is improved.
8. The method for preparing the black surface of the 7-series aluminum alloy by micro-arc oxidation according to claim 1, wherein the workpiece to be treated is a gun or a transmitter.
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